DESCRIPTION

This routine use the fourier transform method to convolve the matrix pointed
to by in_mp with the mask mask_mp, putting the result into *out_mpp. When the
size of the mask matrix is large, the routine is highly recommended when the
mask size is large. Unlike the routine 'convolve_matrix',
'fourier_convolve_matrix' deals with the boundary by padding 0, rather than
by wrapping around the 'in_matrix'.

RETURNS

NO_ERROR on sucess and ERROR on failure.

DISCLAIMER

This software is not adequatedly tested. It is recomended that
results are checked independantly where appropriate.